I want to pressurize a cryogenic liquid (LN2 in this test. Eventually LOX). I have a setup similar to this and follow a similar procedure to what is described, but I don’t see the same tank pressure behavior.

Instead, the curve looks like this, where “set pressure” is the pressure reading just after the pressurant regulator set to 700psi. T=12 is when the pressurization begins. T=40 is when expulsion begins. A check valve is in place so no gas flows back into the pressurant bottle. Notice how the tank pressure does not level-off at equilibrium at T=22. Tank pressure will continue to rise beyond, and I started expulsion before it could rise too high. It was observed previously that if I did not start expulsion it could rise past 1100psi.

Any idea what is going on? I am aware of “collapse factor” of pressurants for cryogens but the behavior should not be dissimilar from the first picture.

  • $\begingroup$ is your pressure relief valve working correctly? $\endgroup$ – Hobbes Jan 17 '19 at 10:07
  • $\begingroup$ I read half way before realizing this is not a hypothetical question! ;-) $\endgroup$ – user2705196 Jan 17 '19 at 13:15
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    $\begingroup$ Is this off topic? Cryogenics is related but it's not really a question about space exploration. $\endgroup$ – GdD Jan 17 '19 at 13:22
  • $\begingroup$ @GdD Not sure. On the other hand, this reads more like an engineering problem then Space Exploration, on the other hand there is a significant overlap between those topics. Might be appropriate to discuss this on Meta, not in comments, though. $\endgroup$ – Polygnome Jan 17 '19 at 14:06
  • $\begingroup$ The pressure in the "expected behavior" graph continues to rise as well. Exactly what differences are you asking about? $\endgroup$ – Organic Marble Jan 17 '19 at 14:30

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